58 BOTANICAL GAZETTE [JULY 
The location of the cells can be determined easily in the transverse 
section of the stem, due to the fact that the walls stain a deep blue 
with haematoxylin, and in the longitudinal section the characteris- 
tic shape of the parenchyma cells as contrasted with the tracheids 
make them easily recognizable. 
We find then in the normal stem of Taxus the condition which we 
should expect as the ultimate result of the gradual reduction of 
resin canals, namely, resiniferous parenchyma which finally com- 
pletely disappears except in the case of conservative organs. 
There are three important principles of evolution which have to 
be considered in working out the ancestry of any group of plants, 
namely, the principles of recapitulation in the development of the 
embryo and seedling stages of the plant; retention of ancestral 
characters in the more conservative regions of the plant, as the root, 
leaf, and reproductive axis; and reversion to ancestral conditions 
through injury. 
The first of these principles I have not been able to demonstrate, 
as I did not have access to the seedling stages of the genera investi- 
gated. The principle of the retention of ancestral characters in the 
most conservative organ of the plant is very clearly evidenced in the 
root of Taxus cuspidata by the presence of resin parenchyma cells 
which have entirely passed out of the stem; and finally the presence 
in abundance of resin parenchyma in the wounded stem of Taxus 
baccata seems to show clearly that we have in this instance a rever- 
sion to the ancestral condition. 
From a consideration of these facts the evidence seems to justify 
the conclusion that the Taxineae are the most modern group of 
conifers; that of the Taxineae, Cephalotaxus is the most primitive, 
in most nearly resembling Podocarpus in the abundance of resin 
parenchyma; that Torreya is the intermediate genus in the group, as 
shown by the reduction of resin parenchyma, especially in the stem; 
and that Taxus is the most modern genus in the group, since we find 
here entire absence of resin parenchyma in the stem, although it is 
retained in the root. 
Summary 
1. Resin parenchyma is present in abundance in the stem and 
root of Cephalotaxus drupacea and shows clearly its close relationship 
